This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. The advent of combination antiretroviral therapy (ART) has significantly decreased the morbidity and mortality associated with HIV disease. However, many patients who achieve undetectable plasma HIV-1 RNA levels following treatment ultimately experience virologic failure requiring a change in their ART. Newer agents, particularly those with activity against viral isolates with resistance to currently available drugs, are clearly needed in order to extend the armory of products available to treat patients with HIV-1 infection. The nucleoside reverse transcriptase inhibitors (NRTIs) are important components of the current strategies to control HIV-1 infection. A new, well tolerated cytidine analog with an improved resistance, efficacy and safety profile would make a substantial addition to the therapeutic options for treatment experienced patients with HIV-1 infection. The objective of the study is to compare the antiretroviral efficacy of ATC to lamivudine (3TC) in treatment experienced, HIV-1 infected patients with the M184V/I mutation in reverse transcriptase.? To compare the safety and tolerability of ATC to lamivudine (3TC) in treatment experienced, HIV-1 infected patients. Patients will be randomized to one of 3 Arms to receive for up to 48 weeks in a 1:1:1 ratio: A: apricitabine 800mg BID (plus lamivudine placebo), orally B: apricitabine 1200mg BID (plus lamivudine placebo), orally C: lamivudine 150mg BID (plus apricitabine placebo), orally This study will help determine if this treatment option is effective.